Conflict's costs - from $6.77 meals to billions for rebuilding - are hard to predict.
In 1966, the Pentagon offered an estimate of what the Vietnam War would cost. When America pulled its troops out in 1973, the tab was 90 percent higher - $111 billion.
The Civil War, similarly, cost the North 13 times the original estimate of President Lincoln's Treasury secretary.
As the United States launches its first major war effort of the 21st century, history suggests one financial fact to bank on: The cost will be higher than forecast.
Of course, this conflict, in which the world's most sophisticated weapons are aimed at the leader of a nation with vastly inferior military capabilities - is not your typical war. Uncertainties, ranging from a quick toppling of the regime to an expensive peacekeeping aftermath - could push the tab higher or lower than even the most careful estimate.
So far, the Bush administration itself has not provided an official estimate. The White House may fear a public forecast will create a negative climate of opinion toward the war. Already, the war is seriously jeopardizing the chances of President Bush's proposed $726 billion tax cut passing. Even some Republicans in the Senate are talking about cutting that amount in half.
Nonetheless, the Defense Department and White House budget officials have been preparing a supplemental spending request. Early reports suggested it could be in the $60 billion to $95 billion range for one year, to be submitted to Congress once war starts. It would cover the war, some aftermath costs, and extra terror-war expenses.
The total tab is made up of items small and big, multiplied many times:
• About $10,000 to 15,000 per hour for a bomber run, depending the plane.
• $6.77 for each "meal ready to eat" for soldiers in the field
• $21,000 or so to convert a gravity bomb into a satellite-guided JDAM bomb.
• About $1 million for each Tomahawk cruise missile.
• $3 million a day to deploy an aircraft carrier battle group (the number deployed has gone up because of the war).